The invention relates to a device for the dosing and distribution of a hotmelt on a substrate.
A device is known which comprises a hotmelt distribution pipe extending over the entire length of a stencil along a squeegee element. The distribution pipe is provided with a large number of outflow apertures situated next to each other in the longitudinal direction. During operation, the hotmelt is supplied to one side of the distribution pipe. The outflow apertures situated next to each other have cross sections that increase by a certain step size, viewed in a direction downstream of the hotmelt supply side. This is an attempt to compensate for the fall in pressure of the hotmelt in the distribution pipe and to obtain a substantially uniform distribution of hotmelt.
A disadvantage in the case of this known device is that, depending on the type of hotmelt and the hotmelt temperature to be applied, an appropriate distribution pipe with a specific distribution and step size in outflow apertures must be used. The hotmelt temperature in particular can vary greatly, and consequently so can the viscosity of the hotmelt. Furthermore, depending on the application width on the substrate, an appropriate length of distribution pipe must be selected. This means that a user soon needs several different distribution pipes. It has been found in practice that the distribution of the hotmelt leaves much to be desired. On completion of a distribution cycle and/or on changing over to another type of hotmelt and/or on changing over to another distribution pipe, the entire hotmelt contents of the distribution pipe are lost. In particular, when a reactive hotmelt is being used, for example a hotmelt that hardens irreversibly on contact with air, special measures have to be taken to prevent undesirable permanent hardening of the hotmelt. For instance, during a fairly long stop or during storage of the distribution pipe, the distribution pipe must be placed in a solvent, or the distribution pipe must be filled with a purge, for example a thermoplastic hotmelt that stops the reaction process of the reactive hotmelt. This again leads to large quantities of hotmelt being lost.
Furthermore a device is known from DE-C-197 36 563. This device comprises a stencil inside which a squeegee, a hollow profile element for the distribution of hotmelt and a profile element with a heating element for the heating of the hotmelt are positioned. The profile elements are positioned on opposite sides of the squeegee and extend over substantially the entire length of the squeegee, thus clamping the squeegee in between. The hollow profile element is rectangular in cross-section and is provided in its bottom wall with a large number of outflow apertures situated next to each other in the longitudinal direction.
A disadvantage of this known device is that depending on the desired application width, the type of hotmelt and hotmelt temperature to be applied, an appropriate assembly of squeegee and profile elements must be used. In practice it is suggested for this type of device to close the outflow apertures all together airtight by means of an adhesive metal tape, should a long stop or storage of the assembly be envisaged. Thus it is hoped to prevent undesirable hardening of the hotmelt inside the hollow profile element. This taping process is time consuming since it is necessary to remove the entire assembly out of the stencil before being able to adhere the tape. During the removal of the assembly, there is the risk of hotmelt dripping out of the outflow apertures at undesirable places. A compensation for the fall in pressure of the hotmelt in the hollow profile element during use, is not provided for, leading to a not uniform distribution of hotmelt.
The object of the present invention is to provide a device in which the above mentioned disadvantages are overcome, and in particular to provide a device by means of which at different application widths and/or with different types of hotmelt optimum hotmelt distribution can be obtained in a flexible manner with one and the same distribution system.
This object is achieved according to the invention by a device for dosing and distribution of hotmelt on a substrate, comprising substrate throughput means, hotmelt supply means, and at least one hotmelt application position with a stencil, hotmelt distribution means and a squeegee device, said hotmelt distribution means comprising a hotmelt dispensing nozzle, wherein a dosing unit and drive means for moving said dosing unit to and fro along said squeegee device are provided, said hotmelt dispensing nozzle being fitted on said movable dosing unit. The device has at least one hotmelt application position for applying hotmelt to a substrate. This device can be designed both for the application of a hotmelt print and for the application of a hotmelt coating. The application position comprises a stencil and a squeegee device, and a dosing unit that is movable along the squeegee device. The dosing unit comprises a nozzle for dispensing hotmelt. The nozzle is in flow or fluid communication with hotmelt supply means. The hotmelt supply means are designed to follow the movement of the dosing unit and comprise heating means for keeping the hotmelt at the correct temperature. The dosing unit can be moved to and fro along the squeegee device by means of conveyor means and at the same time, by means of a suitable control of the supply means, can dispense a desired quantity of hotmelt at the position of a squeegee element of the squeegee device. The squeegee element presses the hotmelt through the stencil onto the substrate. Thanks to the movable dosing unit, the hotmelt can be distributed very accurately over the length of the squeegee device. The quantity of hotmelt dispensed and the application width over which the dosing unit is moved to and fro can be adjusted accurately in a simple manner. This makes the device flexible and cheap to use, and in particular readily adaptable to various types of hotmelt, different hotmelt temperatures and different application widths. Moreover, the dosing and distribution is reliable, partly due to the fact that the nozzle can be designed with a relatively large cross section, which minimizes the risk of blockage. At the end of a distribution cycle and/or on changing over to another printing width, little or no hotmelt need be lost. It is advantageous that no expensive and time-consuming measures need be taken when a reactive hotmelt is being used.
In particular, the device further comprises purge supply means, and the dosing unit is further provided with a purge dispensing nozzle that is in flow or fluid communication with the purge supply means. This means that after the completion of a distribution cycle a quantity of purge can be distributed over the length of the squeegee device using one and the same movable dosing unit. This is important particularly if a reactive hotmelt has been used. The purge flushes the reactive hotmelt out of the stencil and the squeegee device and further prevents the reactive hotmelt from undesirably continuing its reaction.
More particularly, the above mentioned purge dispensing nozzle is disposed in such a way that said nozzle opens out in the hotmelt dispensing nozzle, near the free end thereof The supply of a small quantity of purge then suffices to expel the hotmelt from the front part of the hotmelt dispensing nozzle and to cause a sealing plug of purge medium to form there. The sealing plug prevents the hotmelt from continuing its reaction, so that it cannot, for example, further irreversibly harden to the air. In this variant of an embodiment the purge can be formed, for example, by a thermoplastic hotmelt. The formation of a sealing plug of purge medium advantageously also occurs automatically if fairly large quantities of purge are metered along the squeegee device.
The invention also relates to a movable dosing unit for the above stated device, an assembly of such a dosing unit with a squeegee device for the above stated device, and a method for applying a hotmelt to a substrate with the above stated device.